Although slide fasteners represent a highly developed art, for the most part they are composed of certain basic elements which can be easily described. A typical slide fastener thus may have a coupling chain or coupling element formed with a row of spaced-apart coupling heads adapted to interdigitate with the coupling heads of an opposing row upon movement of a slider along these rows, the slider serving to bring about the interengagement of the coupling heads of the two rows or the disengagement thereof, depending upon the direction in which the slider is moved.
The coupling head may be shaped to fit between the coupling heads of the opposing row and to engage therebehind to lock the two rows together until the slider is moved along these rows in a fastener-opening manner.
The coupling chains may be fabricated from a continuous member, e.g. a synthetic resin monofilament in a coil or meander configuration, by complex shaping steps, or may be produced by molding from synthetic resin materials such that the coupling heads are formed unitarily with bridges between successive heads, or such coupling heads may be stamped or otherwise formed from metal. Whatever the case with respect to fabrication of the coupling heads, for most purposes they are strung together in a chain either by being formed unitarily with the bridging elements or by being attached thereto.
Bridging elements generally are flexible and can be composed of synthetic resin material as already indicated or even can be cords onto which the coupling heads are molded or to which the heads may be secured, e.g. by clamping.
The fabrication of a chain of spaced-apart coupling heads ensures maintenance of the interhead spacing for further handling of the coupling chain as, for example, when the latter is to be applied to a flexible support.
Flexible supports of various types can be provided and, since the present invention is concerned with supports to which the coupling chains are attached by sewing, the present discussion will be confined to these.
For example, one type of support is a fabric tape along an edge of which the coupling chain may be stitched, this tape and row of coupling heads forming a so-called stringer half. Two such halves, positioned so that the rows of coupling heads can interdigitate and provided with a slider and end stop members, if desired, make up a slide fastener stringer.
However, it is frequently desirable to apply the coupling chains directly to two edges of a workpiece to be joined. For example, an opening in a fabric workpiece may have opposite edges provided directly with the coupling chains when it is inconvenient or uneconomical to sew respective stringer halves to the fabric workpiece or garment.
It is also desirable in other cases to attach the coupling chain directly to an edge of a flexible workpiece.
There are systems which have been developed for this purpose, e.g. as described in German patent documents DE-AS No. 23 26 421 and DE-OS No. 28 11 834, in which a sewing machine is utilized to attach the coupling element or chain to the fabric workpiece.
For the purposes of this discussion, the term "coupling chain" will be utilized to refer to a single row of coupling heads, interconnected or linked flexibly so that the spacing between these heads is substantially fixed and the entire row of heads can be fed to a stitching location for the attachment to the support by stitches formed at this location, e.g. via the multiple passes of a sewing machine needle which pierces the support between the coupling heads and then is retracted to permit advance of the workpiece and the coupling chain.
In general, these earlier systems operate at great speed utilizing a common feeder or transport for the fabric and the coupling chain. For example, this feeder may be the fabric feed dogs of the sewing machine beneath the stitching plate.
The support provided with a coupling chain in this manner and by these devices, however, is found to develop undulations or corrugations which result apparently from uncontrolled differences in the tensioning or movements of the fabric and the coupling chain. Frequently these defects develop or are noticeable only after the garment, workpiece or other structure produced by attaching the coupling chain to the support has been subjected to a subsequent treatment.